1. Field of the Invention
The present invention relates to a method for forming layers and patterns of nanowire and/or nanotube using a chemical self assembly, and a method for fabricating a liquid crystal display device employing the same, and particularly, to a method of forming layers and patterns of nanowire and/or nanotube using a chemical self assembly for forming a semiconductor layer of a thin film transistor or the like by using a nanowire and/or nanotube solution and an diamine-based self-assembled monolayer (SAM) material, and a method for fabricating a liquid crystal display device by employing the same.
2. Discussion of the Related Art
Nanowires can be divided according to their electrical characteristics into various types, including, for example, metallic nanowire, semiconductor nanowire, and ferrite nanowire. A variety of materials have been reported, as the metallic nanowire, including silver (Ag), gold (Au) and tungsten (W). Also, the semiconductor nanowires representatively include zinc oxide (ZnO) nanowire, gallium nitride (GaN) nanowire and silicon (Si) nanowire. The semiconductor nanowire generally has a diameter less than 100 nm, and a band gap of the semiconductor nanowire can be controlled in the range from 1.1 eV to 3.4 eV, thus to be widely applicable as a material of optical elements, switching devices and the like.
Research has been conducted for carbon nanotube since Dr. Iijima of Meijo University in Japan, who studied an electron microscope, discovered it in 1991. The carbon nanotube has the form of a rolled graphite sheet, and typically has a diameter of 1˜20 nm. The graphite has a unique coupling arrangement so as to be in the form of a strong, flat, hexagonal plate film. Upper and lower portions of this film are filled with free electrons. Such free electrons perform a parallel motion with the film in a discrete state. The graphite sheet is spirally rolled up to define a carbon nanotube. Accordingly, an edge coupling is executed at different points. When the spiral shape or chirality of the tube is changed, the free electrons move in a different manner.
Thus, the motion of the free electrons becomes completely free, which requires the nanotube to react like a metal or overcome a band gap like a semiconductor. The size of the band gap depends on a diameter of tube. The diameter of tube can be as small as 1 eV. As such, the carbon nanotube has mechanical rigidness and chemical stability and also can have properties of both semiconductor and conductor. Also, in view of its characteristics of small diameter, long length and hollow shape, the carbon nanotube is widely used as a material of flat panel display devices, transistors, energy storages and the like. In addition, it can be applicable to a variety of nano-sized electric devices.
As methods for arranging the carbon nanotube on a base (or substrate), there have been reported a method for substituting an end of carbon nanotube with sulfur so as to arrange on gold by Zhongfan Liu, et al (Peking University, China) (Langmuir, Vol. 16, p. 3569 (2000)), and a document disclosing that carboxyl group (—COOH) reacts on an amine-processed substrate using amide for perpendicular arrangement (Chemphyschem 2002, No. 10). Also, for patterning carbon nanotube, several methods are employed, including a method, reported in Chemical Pysics Letters 303, p. 125 (1999), in which a self-assembled monolayer (SAM) of trimethylsilyl is formed on a silicon substrate to be patterned using e-means, and an amine group is adsorbed on the thusly-generated patterns so as to adsorb the carbon nanotube on the patterns, a simple adsorption method using an interfacial characteristic as reported in Advanced Materials 2002, 14, No. 12, p. 899, and the like.
In addition, a method for forming a carbon nanotube layer and patterns using a chemical self-assembly is disclosed in U.S.A. Laid-Open Publication No. U.S. Pat. No. 6,960,425. Explaining essential contents of the method, the surface of a substrate, such as a silicon wafer or a plastic, is made to be terminated with amino group (—NH2) using a first self-assembled monolayer (SAM) material, for example, aminocarboxylic acid, aminocarboxyl siloxane or diamine. Next, a second SAM material, such as a carbon nanotube solution, prepared by coupling the aminocarboxylic acid to the carbon nanotube to make an acid radical of the carbon nanotube ended with carboxyl group (—COOH), is formed onto the base having the surface terminated with the amino group (—NH2) to fabricate the first carbon nanotube film.
A third SAM material, such as a diamine-based SAM material, is coated such that the surface of the first carbon nanotube film formed on the substrate is aminated (—NH2) again. Afterwards, the second SAM material, such as the above carbon nanotube solution or the like, is formed on the substrate, to fabricate the second carbon nanotube film.
Such processes are repeated to control the thickness per each layer.
However, the method requires complicated processes during the SAM processing on the surface of the carbon nanotube, which causes an increase in a tact time, resulting in a yield decrease. Also, the process for aminating (—NH2) the surface of the carboxyl group (—COOH) is further performed, thereby further requiring the tact time.
Furthermore, a device characteristic is deteriorated on the surface of the carbon nanotube due to SAM polymerization and non-uniformity of concentration. A conductance is also affected by an increase in carbon content, causing a deterioration of a peculiar property of the carbon nanotube.